This invention concerns electronic circuitry for regulating, in a predetermined way, an output voltage that is produced by a direct current power source having a discharging voltage characteristic. The invention particularly concerns simple, economical circuitry for regulating an output voltage produced by a single cell battery that powers an electrical load and also powers the regulating circuitry.
Battery powered electrical apparatus is pervasive. In many applications, batteries are installed and the apparatus is used until the batteries are exhausted, when they are replaced. With many kinds of electrical or electronic apparatus, the gradual decline of battery voltage as the battery discharges does not significantly affect performance of the apparatus. In other electrical or electronic devices, a decline in battery voltage directly influences some operating characteristic. For example, where a battery, such as a common D-size cell, drives a direct current motor, the motor speed will decline as the battery discharges and its voltage decreases.
In one battery powered apparatus of particular interest a single cell battery continuously operates a direct current fan motor blowing air over a controlled volatility odor control product. Periodically the odor control product is replaced and, preferably, at the same time, the battery is replaced. In order to dispense the odor control product at a substantially constant rate, assuming no change in its volatility, it is necessary to maintain the fan at a substantially constant speed between battery changes If the odor control product volatility decreases as its source is depleted, it is desirable to increase the fan motor speed as the time for battery replacement grows closer. To achieve these respective ends, the voltage supplied to the motor from the battery must remain substantially constant or increase with time while the battery is discharging and its voltage is decresing.
While voltage regulators are commonly used to produce a substantially constant output voltage from a varying amplitude input voltage, regulating the output voltage from a low voltage discharging source, such as a single cell battery, is a challenging task. The total amount of power available to operate both the regulator and other apparatus is limited by the battery source. The amount of energy consumed by the regulator must be minimized so as not to shorten battery life unduly. Moreover, the voltage difference between that applied to the electrical load and the battery voltage (including the difference between the fully charged battery voltage and the discharged battery voltage) must be minimized so that sufficient voltage is available to operate an electrical load. Finally, apparatus intended to be operated by a single cell battery is likely to be lightweight and inexpensive. Therefore, a regulator powered by and regulating the voltage from the cell must also be lightweight and inexpensive to be practical.